spontaneous fission


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spontaneous fission

[spän′tā·nē·əs ′fi·shən]
(nuclear physics)
Nuclear fission in which no particles or photons enter the nucleus from the outside.
References in periodicals archive ?
(a) denotes the emitting time of [sup.252]Cf spontaneous fission. (b) shows the directly transmitted gamma rays recorded by the detector.
When [sup.252]Cf spontaneous fission, directly transmitted neutrons, the scattered neutrons, and the neutrons from induced fission all are detected by the detector, the peaks appeared in the curve.
The average energy of [sup.252]Cf source spontaneous fission neutron is 2.13 MeV.
The apatite crystals were sealed in epoxy resin, polished, etched with a 2.5% HN[O.sub.3] solution for 70 s at 22 [degrees]C to enable visibility of the spontaneous fission tracks, fitted with a muscovite external detector (Miller et al., 1993) and irradiated in a nuclear reactor (Oregon State University Radiation Center) by thermal neutrons.
Nonetheless, chain reactions do occur in SNM, triggered by a neutron from spontaneous fission or a background neutron.
The fission-track age is calculated from the fraction of decays of [sup.238]U that produce a fission track within a given volume of sample; the amount of [sup.238]U in the sample volume; the areal density of fission tracks on a polished surface produced by spontaneous fission of [sup.238]U in the natural sample; the areal density of fission tracks on the polished surface that have been induced by irradiation of [sup.235]U in the sample by thermal neutrons; the thermal neutron flux of the reactor in which the sample is irradiated; and the capture cross-section of 235U for thermal neutrons.
The researchers also look for evidence of new isotopes, in which the number of neutrons present in a nucleus differs from known varieties, and for traces of spontaneous fission, in which a newly synthesized nucleus immediately splits into two pieces.
The transuranics are all inherently unstable, subject to spontaneous fission or radioactive decay -- as is uranium, atomic number 92, the heaviest element known to exist in detectable amounts on earth.
In the end they discovered instances of spontaneous fission that did not correspond to anything they could identify.

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